The invention relates to techniques for determining the specific resistance of a test sample, such as a silicon disc, and more particularly to techniques of this type which perform such measurements without the necessity of contact with the surface of the test sample.
Commonly known techniques of this latter type conventionally operate by sensing the change in voltage of a resonant circuit when a pair of specified terminals of such circuit is coupled to a test probe that is brought into reactive coupling relation with the test sample. Such known circuits have the disadvantages of being relatively time-consuming in operation and complicated in form, due to the necessity of providing special indicator scales or correction diagrams to compensate for observed non-linearities between variations in the specific resistance of the test sample and the resulting variations in voltage at the output of the measuring circuit. In addition, the accuracy of such known techniques is not only low in an absolute sense, but also varies as a function of the then-occurring magnitude of the specific resistance of the test sample.